1. INTRODUCTION

The direct ancestors of the dinosaurs (early Archosaurs) and mammal-like reptiles (Therapsids) originated within 10 million years of each other within the Triassic Period of the Mesozoic Era. They co-existed for some 30 million years along with the reptilian ancestors of modern-day crocodiles. The reptiles with diverse body types were more successful than early dinosaurs and mammals during this time.

At the End Triassic (Tr-J) extinction, the crocodile relatives (reptiles) were almost completely gone and the dinosaurs began their 135 million-year domination on our planet.

“Stiff Competition: For much of the Triassic period dinosaurs (and mammals) were a marginal group, overshadowed by the likes of crocodile relatives such as Saurosuchus (1) and giant amphibians such as Metoposaurus (2). Credit: Ricardo N. Martínez Institute and Museum of Natural Sciences, National University of San Juan (1); Tomasz Sulej Institute of Paleobiology, Polish Academy of Sciences (2)” (Scientific American May 2018)

Phytosaurs are an extinct group of large, mostly semiaquatic Late Triassic archosauriform reptiles. Phytosaurs belong to the family Phytosauridae and the order Phytosauria (dinosaur predators).

After the Cretaceous-Paleogene (K–Pg) extinction 66 million-years-ago, the non-avian dinosaurs were completely gone and mammals began their domination of our planet.

This artist’s rendering of the hypothetical placental ancestor – the Common Ancestor of all Placental Mammals – was surviving in the Tertiary environment of 65 million years ago. With the demise of their dinosaur predators, mammal evolution accelerated. (Image courtesy of Carl Buell)

The following physical, chemical and biological alterations occurred on our planet during the Tr-J and the K-Pg extinctions:

IMPACT CRATERS: an approximately circular depression in the surface of a planet, moon, or other solid body in the Solar System or elsewhere, formed by the hypervelocity (>12km/sec) impact of a smaller body.

IMPACT EJECTA: a special group of sediments comprising material that is thrown out from an impact crater in the excavation stage and deposited at a distance determined by the size of the impact.

IRIDIUM (Ir) CONCENTRATIONS: “Iridium is one of the rarest elements existing in two parts per billion in the Earth’s crust. Iron meteorites contain about 3 parts per million of iridium. Stony meteorites contain about 0.64 parts per million of iridium” (Chemistry Explained).

VOLCANIC ACTIVITY: “In geology, a large igneous province (LIP) is an extremely large accumulation of igneous rocks, including plutonic rocks (intrusive) or volcanic rock formations (extrusive), arising when hot magma extrudes from inside the Earth and flows out. The source of many or all LIPs is variously attributed to mantle plumes or to processes associated with plate tectonics (Foulger 2010)”. Traps, the Swedish word for stairs, refers to the stepped appearance of lava flows that oozed from a vast rift in the Earth’s crust for nearly a million years.

CLIMATE CHANGE: a change in the statistical properties (principally its mean and spread) of the climate system when considered over long periods of time, regardless of cause.

The K-Pg extinction that ended the non-avian dinosaurs is well explained. But there is a mystery of how the reptiles lost their domination at the Tr-J extinction allowing the dinosaurs to dominate.

My article documents the influence the two separate extinctions had on the physical, chemical and biological alterations on our planet and their common characteristics.

2. K-Pg & Tr-J GEOMORPHOMETRY COMPARISONS

CRETACEOUS-PALEOGENE (K–Pg) – 66.043 ± 0.011 million-years-ago:

IMPACT CRATER:

“The K–Pg extinction event, a sudden mass extinction of some three-quarters of the plant and animal species on Earth, was caused by a large bolide impact. In 1990 Hildebrand et al. showed that the source crater for the K-Pg extinction is probably the 180-km-diameter Chicxulub crater which lies on the Yucatan Peninsula, Mexico. Non-avian dinosaurs did not survive this event” (Hildebrand 1993).

“Knowing the size and location of the crater allows well-constrained modelling of the lethal effects of the impact. The Chicxulub impact produced a massive pulse of shock-devolatized CO2 and SO2 because the target rocks included a thick sequence of carbonates and sulphates. It was therefore particularly lethal for an impact of its size” (Hildebrand 1993).The Chicxulub Impact Crater is illustrated here immediately over the horizon . I took this image during a cruise just to the east of the impact site. I stood on my tippy-toes to try and get the crater over the horizon only to be photo-bombed by a whale. If I was at this location 65 million years ago during the impact, either the extreme heat shock wave of asteroid atmosphere contact/entry, or the impact explosion or the tsunami hundreds of metres high would have made a very bad day for me.

IMPACT EJECTA:

“The K-Pg boundary clay is known to consist of two layers:
– a globally-distributed, uniform ~3-mm-thick layer which was probably dispersed by the impact fireball and
– a layer found only near the source crater composed of ballistically-distributed ejecta.
Chondritic siderophile trace -element anomalies, shocked minerals and tektites have been subsequently found in the K-Pg boundary layers” (Hildebrand 1993).

br Close-up of the Cretaceous–Paleogene (K–Pg) boundary, formerly known as the Cretaceous–Tertiary (K–T) boundary – at the Royal Tyrrell Museum, Drumheller Alberta. (Image by the author)

IRIDIUM (Ir) CONCENTRATIONS:

“The mass of the Chicxulub asteroid is calculated to be about 300 billion metric tons with an asteroid diameter 10 ± 4 kilometers (km), determined from the iridium measurements in the K-Pg boundary (about 100 times natural concentrations), the concentration of iridium in so-called chondritic meteorites and the surface area of the Earth, ” (Alverez 1997).

“THE IRIDIUM ANOMALY: The levels of iridium across the Gubbio formation are plotted. Note the spike in the K-T boundary clay.” (Alverez)

VOLCANIC ACTIVITY:

The Deccan Traps began forming 66.25 million years ago at the end of the Cretaceous period. This series of eruptions may have lasted less than 30,000 years in total.

The lava flows covered 1.5 million km2 of western India with multiple layers of solidified flood basalt more than 2,000 m thick. The Deccan Traps region was reduced to its current size by erosion and plate tectonics; the present area of directly observable lava flows is around 500,000 km2.

The Chicxulub asteroid impact and the eruption of the massive Deccan volcanic province are two proposed causes of the end-Cretaceous mass extinction, which includes the demise of nonavian dinosaurs.

“U-Pb zircon geochronology of Deccan rocks show that the main phase of eruptions initiated ~250,000 years before and continued for 500,000 years after the Cretaceous-Paleogene boundary. More than 1.1 million km3 of basalt erupted in those ~750,000 years. The Deccan Traps contributed to the latest Cretaceous environmental change and biologic turnover that culminated in the marine and terrestrial mass extinctions.” (Schoene 2015)

“There is evidence for the triggering of magmatism on a global scale by the Chicxulub meteorite impact at the Cretaceous-Paleogene (K-Pg) boundary, recorded by transiently increased crustal production at mid-ocean ridges. Concentrated positive free-air gravity and coincident seafloor topographic anomalies, associated with seafloor created at fast-spreading rates, suggest volumes of excess magmatism in the range of ~105 to 106 km3. Widespread mobilization of existing mantle melt by post-impact seismic radiation can explain the volume and distribution of the anomalous crust. This massive but short-lived pulse of marine magmatism should be considered alongside the Chicxulub impact and Deccan Traps as a contributor to geochemical anomalies and environmental changes at K-Pg time.” (Byrnes 2018)

“The Chicxulub impact produced a massive pulse of shock-devolatized CO2 and SO2 because the target rocks included a thick sequence of carbonates and sulphates and was therefore particularly lethal for an impact of its size. The addition of these gases to the atmosphere led to a global sulphurous acid rain and a long-term CO2 greenhouse warming of ~10° Celsius. The Chicxulub impact was orders of magnitude more deadly to the environment than any known terrestrial process such as volcanism. Extinction-causing impacts of this size reoccur approximately once every 100 million years thereby altering the long-term evolution of life on earth” (Hildebrand 1993).

TRIASSIC-JURASSIC (Tr-J) – 237-201.3 million-years-ago:

IMPACT CRATERS:

Dated within the 237-201.3 million-year time frame of the End Triassic, many large bolide impacts have been identified at present-day northern latitudes. They range from 9 to >100 km in diameter.

The presence of impact structures with Late Triassic ages suggests the possibility of bolide impact-induced environmental degradation prior to the end-Triassic.

“The attempts to establish a globally significant causal extinction connection between the larger impacts (e.g. Manicouagan and Rochechouart) and Late Triassic marine and terrestrial bioevents (culminating with the End Triassic Extinction), have proved unsuccessful” (Clutson et al 2018).

The Manicouagan impact crater looking east as seen from GOZooM. At this distance seeing the crater for the first time, I was “impressed” by the size of this structure. Image by the author from C-GOZM.The Dauphin river is illustrated paralleling the northern rim of the St. Martin impact structure as it flows into Lake Winnipeg. Image by the author from C-GOZM.Red Wing structure – the superimposed circle illustrates the position of the buried crater. This image, aimed looking east at the approximate point of impact, was taken from GO ZooM at approximately 4500 feet AGL. Image by the author from C-GOZM.

IMPACT EJECTA:

214 Ma – LATE TRIASSIC EJECTA – SW BRITAIN
“The documented late Triassic spherule layer of SW England deposit contains an abundance of spherules, common shocked quartz and a suite of accessory minerals believed to have been derived direct from the impact site. These include garnets, ilmenites, zircons and biotites. Garnets and ilmenites are highly fractured, and biotites show prominent kink bands indicative of shock” (Thackrey 2009) .

“The Late Triassic ejecta deposit of SW Britain where impact melt spherules have been completely altered to clay. Radiogenic dating of this deposit shocked biotites (observed exclusively in this Late Triassic ejecta deposit) yielded ages consistent with the Grenvillian target rocks at Manicouagan” (Thackrey 2009).

IRIDIUM (Ir) CONCENTRATIONS:

“New analyses confirms Ir enrichment (up to 0.31 ng/g) in close proximity to the palynological Triassic–Jurassic boundary in strata near the top of the Blomidon Formation at Partridge Island, Nova Scotia. High Ir concentrations have been found in at least two samples within the uppermost 70 cm of the formation. There is enrichment of some platinum group elements (including Ir) and transition group elements in strata that occur at, and in close stratigraphic proximity to, the horizon of palynological turnover that is interpreted as the Triassic–Jurassic boundary in the Fundy basin” (Tanner 2005).

Lithostratigraphy of the uppermost meter of the Blomidon Formation and Ir concentrations determined by NAA and ICP-MS analyses. Sample identification numbers demarcate the depth (in centimeters) below the contact with the North Mountain Basalt of the top of the 5-cm sample interval. Ir is plotted as the mid-point of the sample interval. TJB=position of Triassic–Jurassic boundary as determined by palynology [12]. NA=sample not analyzed; BD=concentration below detection limit.

VOLCANIC ACTIVITY:

Two volcanic episodes in the Triassic are significant to dinosaur evolution:

1. “The Central Atlantic Magmatic Province (CAMP) is the Earth’s largest continental large igneous province, covering an area of roughly 11 million km2. It is composed mainly of basalt that formed prior to the breakup of Pangaea near the end of the Triassic and the beginning of the Jurassic periods.

The Tr-J multi-sized impact events formed prior to commencement of the CAMP volcanic episode by several million years.

214 Ma – CENTRAL ATLANTIC MAGMATIC PROVINCE (CAMP) and BAY OF FUNDY

Widespread eruptions of flood basalts of the Central Atlantic Magmatic Province (CAMP) were synchronous with or slightly postdate the Late Triassic boundary” (Tanner 2004).

“Location and geologic map of the study area in the Fundy basin. Samples analyzed in this study were collected from Partridge Island, near Parrsboro, Nova Scotia” (Tanner 2005).

“The Bay of Fundy terrestrial redbeds of the Blomidon Formation were deposited during the late Triassic and early Jurrasic. A 10-m-thick zone of intensely deformed strata that occurs near the base of the formation is characterized by faulting. Correlation of this zone basin-wide indicates that it is a record of a very powerful paleoseismic event. The presence in strata just above the deformed zone of quartz grains displaying features of shock metamorphism raises the intriguing possibility that reactivation of the fault zone was triggered by a bolide impact” (Tanner 2002).

Cape Split Bay of Fundy, Nova Scotia, the craggy escarpment which rings this immense gulf was formed during a critical juncture in Earth history called the Triassic-Jurassic boundary, 200 million years ago (Thurston, 1994). The uppermost meter of the Blomidon Formation within this escarpment contains irridium (Ir) concentrations possibly from the Manicouagan impact. Image by the author from C-GOZM.

2. “Wrangellia flood basalts formed as an oceanic variety of a large igneous province (LIP) in the Middle to Late Triassic, with accretion to western North America occurring in the Late Jurassic or Early Cretaceous” (Richards et al., 1991).

The accreted Wrangellia oceanic plateau in the Pacific Northwest of North America is perhaps the most extensive accreted remnant of an oceanic plateau in the world where parts of the entire volcanic stratigraphy are exposed.Prince Rupert, British Columbia, illustrating the mountains, in the background looking north, created by the collision of the Wrangellia igneous province with Canada’s west coast. The Carnian Pluvial Episode (CPE) contemporaneous with this event is coincidental with the rise of the dinosaurs in the late Triassic. Image by the author from C-GOZM.

CLIMATE CHANGE:

“The dinosaurs had a sudden growth in size at the of the end of the Carnian Pluvial Episode (CPE) in the Triassic period. This was a time when climates shuttled from dry to humid and back to dry again.

“At the CPE, the massive eruptions in western Canada, represented today by the great Wrangellia basalts, caused bursts of global warming, acid rain, and killing/extinctions on land and in the oceans” (Bernardi 2018).

It is suspected that the Wrangellia had a telling effect at the CPE and the beginning of the 135 million-year dinosaur domination.

“THE CORRELATION BETWEEN THE EARLIEST DINOSAUR OCCURRENCES ACROSS PANGAEA. Note the synchronicity of the first dinosaur diversification event during and after the CPE (light green boxes)” (Bernardi 2018).

3. CONCLUSION

Cretaceous–Paleogene (K–Pg) – 66.043 ± 0.011 million years ago – the end of the dinosaur era
“Sixty-five million years ago, a comet or asteroid larger than Mount Everest slammed into the Earth, creating the Chicxulub crater, inducing an explosion equivalent to the detonation of a hundred million hydrogen bombs. Vaporized detritus blasted through the atmosphere upon impact, falling back to Earth around the globe. Disastrous environmental consequences ensued: a giant tsunami, continent-scale wildfires, darkness, and cold, followed by sweltering greenhouse heat. When conditions returned to normal, half the plant and animal genera on Earth had perished” (Alverez 1997). The non-avian dinosaurs were now extinct, making way for mammals to evolve and dominate our planet.

Triassic-Jurassic (Tr-J) – 201.3 million years ago: –the beginning of the dinosaur era
For 30 million years primitive dinosaurs and mammals lived alongside giant, crocodile-like animals known as the crurotarsans in the Triassic Period. The reptilian crurotarsans outnumbered the dinosaurs and were even more diverse. At the Triassic–Jurassic boundary 200 million years ago, the reptilian crurotarsans were virtually gone making way for the dinosaurs to evolve and dominate our planet.

Closing argument:

Dinosaurs originated about 245 Ma, during the recovery from the Permian-Triassic mass extinction. They remained insignificant until they emerged in diversity and ecological importance during the Late Triassic Tr-J event, 201 million years ago. Thus began the 135-million-year dinosaur domination of our planet.

At the K-Pg 66 million years ago, a bolide impact ended the reign of the non-avian dinosaurs.

The geomorphometry of the K-Pg and Tr-J events were compared to illustrate their similarities.

“However, the mode and timing of the origin and diversification of the dinosaurs at the Tr-J have so far been unresolved” (Bernardi 2018).

“There is serious debate on whether the ETE actually exists, or whether it was an event that was attenuated over ~40 Ma (almost 2/3 the time span of the Tertiary!)”(David E. Brown – private correspondence 2018).

“The K/T (K/Pg) impact at the End Cretaceous, turned the Earth’s surface into a living hell, a dark, burning, sulphurous world where all the rules governing survival of the fittest changed in minutes. The dinosaurs never had a chance” (Hildebrand 1993). “Accelerated biotic turnover during the LateTriassic has led to the perception of an End-Triassic mass extinction event, now regarded as one of the ‘‘big five’’ extinctions” (Tanner 2004).

4. REFERENCES

PAPERS

Walter Alvarez T. rex and the Crater of Doom University of California, Berkeley (1997)

The Permian is a geologic period and system which extends from 298.9 ± 0.2 to 252.2 ± 0.5 (Million years ago). The Permian–Triassic (P–Tr or P–T) extinction event formed the boundary between the Paleozoic and Mesozoic eras. It is the Earth’s most severe known extinction event, with up to 96% of all marine species and 70% of terrestrial vertebrate species becoming extinct.

Coincidental with the P-Tr extinction, about 2.6 million km2 of 4 km thick basaltic lava covered Siberia in a flood basalt event. The original volume of lava is estimated to range from 1 to 4 million km3 (Wikipedia).
It is unclear whether this magmatism was the main culprit, or simply an accessory to the P-Tr mass extinction.

The Siberian Traps, a deadly epoch of 2.6-million-square-kilometer, 4-kilometer-thick volcanic eruption, left its fingerprint in Siberia and was synchronous with the Permian–Triassic (P-Tr) boundary extinction.

The Triassic is a geologic period and system that extends from about 250 to 200 Ma (252.2 ± 0.5 to 201.3 ± 0.2) million years ago).

The Jurassic is a geologic period and system that extends from 201.3± 0.6 Ma (million years ago) to 145± 4 Ma.The Cretaceous, derived from the Latin “creta” (chalk), usually abbreviated K for its German translation Kreide (chalk), is a geologic period and system from circa 145 ± 4 to 66 Ma (million years ago).